The present application relates to a method for treating carbon nanotubes (CNTs), treated CNTs, and a CNT device using the treated CNTs.
As one-dimensional nano-material, CNTs are of many excellent electrical, mechanical, and chemical properties, and therefore have attracted increasing attention. With the continuing study on this nano-material, the potential various application for the CNTs are continuously arising. For example, the CNTs can be applied in the fields of electronics, optics, mechanics, biotechnology, and ecology, and used in, for example, a nano-field effect transistor, a field emission source, a hydrogen storage material, a high strength fiber, a sensor, and the like.
CNTs can be classified as single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) according to the number of the carbon atom layers forming the wall, wherein the MWNTs may be considered as being formed by nesting the SWNTs with different diameters. In research and application, the SWNTs and the MWNTs with relatively small number of atom layers are of importance due to the outstanding performance.
CNTs can also be classified as metallic CNTs and semiconducting CNTs according to their conductivity, in which the former for example can be used in field emission source, electrode materials and the like, and the latter for example can be used in nano-filed effect transistors, sensors and the like. In Saito R et al, Material Science and Engineering, 1993, B19: 185 to 191, Saito et al. have through theoretical analysis concluded that according to the diameter and chiral angle of the SWNTs, about ⅓ of SWNTs are metallic and the other ⅔ are semiconducting. Due to the various preparing condition, purifying treatment and the like, the ratio of the two types of CNTs may not be strictly consistent with the above theoretical value in the actual prepared product. With the increase of the number of the carbon atom layers, the metallicity of the CNTs gradually increases and at last the CNTs become pure metallic.
The conventional methods for preparing the CNTs include graphite arc-discharging, chemical vapor deposition, laser evaporation and the like. The CNTs obtained through these methods normally include both metallic CNTs and semiconducting CNTs that are mixed together. Therefore, one of the prerequisite for the metallic and semiconducting CNTs being put into application is to separate the CNTs with the different conductivity from each other in the prepared product. Hence, the separation of the CNTs has become one of the important topics in the research.
Currently, many methods using the difference in chemical and physical properties between the metallic and semiconducting CNTs to separate the CNTs have been proposed. For example, in “Engineering Carbon Nanotubes and Nanotube Circuits Using Electrical Breakdown,” Philip G. Collins, et al, Science 2001, 292, 706-709, Collins et al proposed an electrical breakdown method; in “Selective Etching of Metallic Carbon Nanotubes by Gas Phase Reaction,” Guangyu Zhuang, et al, Science 10 Nov. 2006: 974-977, Zhang et al proposed a methane plasma treatment method, in which the metallic CNTs were etched during reaction and the semiconducting CNTs were remained; in “Bulk Separative Enrichment in Metallic or Semiconducting Single-Walled Carbon Nanotubes,” Zhihong Chen, et al, Nano Lett., 2003, 3(9), pp 1245-1249 and in “Dispersion and separation of Small-Diameter Single Walled Carbon Nanotubes,” Yutaka Maeda, et al, J. Am. Chem. Soc., 2006, 128(37) pp 12242, Chen et al and Maeda et al proposed selective absorption methods, respectively; in “Separation of Metallic from Semiconducting Single-Walled Carbon Nanotubes,” Ralph Krupke, et al, Science 18 Jul. 2003:344-347, Krupke et al proposed an electrophoresis method; and in “Sorting carbon nanotubes by electronic structure using density differentiation,” Michael S. Arnold, et al, Nat. Nanotechnol., 2006, 1, pp 60-65, Arnold et al proposed a density gradient centrifugation method.